The objectives of this study are to evaluate whether methylphenidate, a standard treatment for childhood Minimal Brain Dysfunction (MBD), is effective in adults with symptoms considered related to MBD and to evaluate the specificity of drug response. Three groups of patients will be identified and, in a double-blind, crossover design, given 3-week trials of methylphenidate and placebo. The experimental patient group will have adult symptoms of MBD (restlessness, poor concentration, emotional lability, and impulsivity) and childhood histories of MBD symptomatology. One control group will have the same adult symptoms but no childhood histories of MBD; this will control for the possibility that methylphenidate is helpful for certain adult symptoms regardless of childhood history. Another control group will have neither adult nor childhood histories suggestive of MBD, but will have mild-moderate anxiety and depression; this will control for the possibility that methylphenidate is helpful in adults with MBD mainly by a nonspecific antidepressant effect. The overall goal is to determine if MBD is a specific diagnostic entity in adulthood with a specific treatment, stimulant medication. Patient selection will be based on questionnaire data and clinical interviews. Baseline psychological tests will attempt to identify predictors of drug response. Outcome will be evaluated by the psychiatrist, patient, and a significant other.